A fan is used for cooling home appliances, communication equipment, servers, and the like (for example, refer to Japanese Laid-open Patent Application Publications No. 2004-316625 and No. 2003-314499). In the fan disclosed in FIG. 2D of Japanese Laid-open Patent Application Publication No. 2004-316625, so that the openings of the suction opening side and the blowout opening side become wide and the air flow increases, the inner peripheral portion of the casing outer frame of the suction opening side is inclined outward toward the suction opening side, and the inner peripheral portion of the casing outer frame of the blowout opening side is also inclined outward toward the blowout opening side.
Further, in the fan disclosed in FIG. 3A of Japanese Laid-open Patent Application Publication No. 2004-316625, apart from the above description, the inner peripheral portion of the casing outer frame is inclined to the central axis direction toward the blowout opening side from the suction opening side and the air flow is directed to the central axis direction, so that the larger amount of air flow flows to the electronic equipment in the vicinity of the center. In addition, the outer peripheral portion of the base portion hub of the fan of Japanese Laid-open Patent Application Publication No. 2004-316625 is formed in a straight configuration. That is, the outer peripheral portion of the base portion hub is formed in a straight outer diameter shape along the central axis toward the blowout opening.
Further, in the fan disclosed in Japanese Laid-open Patent Application Publication No. 2003-314499, it is intended to widen the opening in the blowout opening side and to increase the air flow volume by inclining the outer peripheral portion of the base portion hub to the central axis direction toward the blowout opening side. In addition, the inner peripheral portion of the casing outer frame of the fan of Japanese Laid-open Patent Application Publication No. 2004-316625 is formed in a straight configuration. That is, the inner peripheral portion of the casing outer frame is formed in a straight inner diameter shape along the central axis toward the blowout opening side from the suction opening side.
Meanwhile, with regard to a fan, a medium air flow volume region (0.5˜1.0 m3/min) is often used as an operating point, and so high static pressure efficiency (=(static pressure×air flow volume)/power consumption) and low power consumption are required in the medium air flow volume region in many cases. As disclosed in Japanese Laid-open Patent Application Publications No. 2004-316625 and No. 2003-314499, if the opening of the blowout opening side is taken wide, in a high air flow volume region where a high air flow volume commensurate therewith is obtained, a corresponding high static pressure is obtained and the static pressure-air flow volume characteristics are improved. As a result, the static pressure efficiency in the high air flow volume region is improved. However, there is a tendency that the static pressure efficiency in the medium air flow volume region is hardly improved, or decreases.
On the other hand, considering the power consumption aspect, if the inner peripheral portion of the casing outer frame of the blowout opening side is inclined outward toward the blowout opening side, as disclosed in FIG. 2D of Japanese Laid-open Patent Application Publication No. 2004-316625, an air flow which spreads outward along the inner peripheral portion is formed. Therefore, the air flow which is ejected from the blowout opening side spreads outward, and so a high air flow volume corresponding to the spent power consumption cannot be obtained.
In addition, if the inner peripheral portion of the casing outer frame is formed in a straight configuration as disclosed in Japanese Laid-open Patent Application Publication No. 2003-314499, That is, the inner peripheral portion of the casing outer frame is formed in a straight inner diameter shape along the central axis as described above, and so the air flow along the inner peripheral portion flows straight along the central axis. Thus, the air flow does not direct the central axis direction, and so the air flow spreads easily toward outside. Then such an air flow which easily spreads outward becomes an air flow which swirls in the vicinity of the blowout opening under the influence of the edge of the inner peripheral portion of the end portion of the blowout opening. The swirling air flow interferes with the air flow which is flowing to the blowout opening direction, and as a result, it becomes a factor of inhibiting the flow (air resistance). When such an air resistance is generated, the load to the motor increases and thus the power consumption increases.
Further, in the configuration shown in FIG. 3A of Japanese Laid-open Patent Application Publication No. 2004-316625, the inner peripheral portion of the casing outer frame is inclined to the central axis direction toward the blowout opening side from the suction opening side, and the air flow which is gotten closer to the central axis direction flows along the straight configuration of the outer peripheral portion of the base portion hub at the center portion. Since the outer peripheral portion has the straight outer diameter shape along the central axis as described above, the air flow along the outer peripheral portion flows straight along the central axis. On the other hand, the inner peripheral portion of the casing outer frame is formed so that the air flow gets closer to the central axis, and so there also exists the air flow which is directed to the central axis direction from outside. In such a case where the straight air flow along the central axis which is present in the inside and the air flow which is directed to the central axis direction from the outside are mixed and the mixed air flows are ejected from the edge portion of the blowout opening, the air flows interfere, and the air flow in the vicinity of the blowout opening is disturbed, and so it becomes a factor (air resistance) of inhibiting smooth ejection of the air flow from the blowout opening. When such an air resistance is generated, the load to the motor increases and the power consumption increases.
Meanwhile, in the configuration shown in FIG. 3A of Japanese Laid-open Patent Application Publication No. 2004-316625, as described above, the straight air flow along the central axis which is present in the inside inhibits the flow of the air flow which is directed to the central axis, and it is considered that the air flow collecting effect to the central axis direction is limited. Therefore, it is estimated that the effect of flowing the air to the electronic equipment in the vicinity of the center is not so large.
From this, in the above described conventional fan, from the view point of the absolute amount of the power consumption, the power consumption increases. Thus, in the case that the above described conventional fan is used in the medium air flow volume region, as described above, there exists a problem that though the static pressure efficiency is hardly improved or decreases, the absolute amount of the power consumption itself becomes larger and the running cost becomes high. Further, from the viewpoint of the cooling capacity, there exists another problem of collecting the air flow to the central axis direction more effectively and sending the air flow to the electronic equipment in the vicinity of the center.